Investigation of pore structure and fracture characteristics of porous rock mass: Computed tomography scan and acoustic emission technology

Abstract

Porous rock masses in mining strata are prone to hazards like water inrush and instability due their developed pore structure and low strength. To investigate the pore structure characteristics and mechanical properties of porous rock mass, computed tomography (CT) scan and uniaxial compression acoustic emission (AE) tests were conducted on cemented broken rock specimens. The results indicated that the Talbot index (η) enhanced specimens porosity and macropore proportion. Connected pores were extracted from the three-dimensional pore distribution, and it was found that the maximum connectivity ratio was a mere 29.3%, suggesting a significant presence of isolated pores within the initial specimens. A pore network model (PNM) was established based on these connected pores. The coordination relationship of the PNM was significantly affected by the volume of the parent pores, while the pore throat radius and throat channel length controlled the distribution of the pore-throat structure in the PNM. As η increased, the uniaxial compressive strength of the specimens first increased and then decreased, accompanied by a transition from tensile to mixed tensile-shear cracks. Post-failure CT scans and three-dimensional cracks reconstruction confirmed this failure transformation: at low η, single tensile cracks with strong connectivity were generated inside specimens, distributed in a vertical lamellar pattern. Conversely, at high η, multiple-structure tensile/shear compound cracks with poor connectivity were formed within the specimens, distributed in disordered lamellar pattern. Finally, a spatial overlap display of the PNM and the three-dimensional reconstructed cracks demonstrated that the crack propagation paths predominantly followed the large pores and coarse throats in the PNM, revealing the spatial consistency between the PNM and crack propagation.